The general objective of this proposal is to assess the merits of employing cognitive self-control training with hyperactive children undergoing maintenance stimulant treatment. The expectation is that cognitive training will affect aspects of cognitive processes not ameliorated by methylphenidate, resulting in improved academic performance. The aims of this proposal are: 1) to determine whether a combination of methylphenidate plus four months of cognitive training can significantly improve academic performance; 2) to determine whether the adjunctive use of cognitive training enables hyperactive children to cope more efficaciously while off medication; 3) to investigate whether any academic gains obtained with this combined approach are maintained after termination of treatment; and 4) to determine whether the combination of both interventions can improve significantly the behavior of children only partially responsive to stimulants. The general experimental design includes the random assignment of children to three treatment groups: 1) Methylphenidate; 2) Methylphenidate plus Cognitive Training; and 3) Methylphenidate plus Attention Control.